migrate to the new for-loop syntax

Drop the ':' before captures (for xs (x) / for 0..n (i)); the index
capture becomes the trailing open range (for xs, 0.. (x, i)). 136
headers across 26 files, mechanical.

Five headless tests (banner_layout, hit_test, swipe_commit,
swipe_intent, swipe_reshuffle) also gain a direct
#import "modules/ui/types.sx" — they named Point/Frame through a
transitive import, which bare visibility no longer permits.

Gates: sx build --target ios-sim main.sx links; tools/run_tests.sh
23/23.

tests/cascade.sx

@@ -24,7 +24,7 @@ EXPECTED_DEPTH :: 2;
 // board can be written as a human-readable grid. The hole glyph maps to `.empty`.
 char_to_gem :: (c: u8) -> Gem {
     if c == EMPTY_CHAR { return .empty; }
-    for 0..GEM_COUNT: (i) {
+    for 0..GEM_COUNT (i) {
         if GEM_CHARS[i] == c { return cast(Gem) i; }
     }
     .red
@@ -34,9 +34,9 @@ char_to_gem :: (c: u8) -> Gem {
 // The RNG is left unseeded — callers seed it before resolving.
 load_board :: (rows: []string) -> Board {
     b : Board = ---;
-    for 0..BOARD_ROWS: (row) {
+    for 0..BOARD_ROWS (row) {
         line := rows[row];
-        for 0..BOARD_COLS: (col) {
+        for 0..BOARD_COLS (col) {
             b.set(col, row, char_to_gem(line[col]));
         }
     }
@@ -44,7 +44,7 @@ load_board :: (rows: []string) -> Board {
 }
 
 boards_equal :: (a: *Board, b: *Board) -> bool {
-    for 0..BOARD_CELLS: (i) { if a.cells[i] != b.cells[i] { return false; } }
+    for 0..BOARD_CELLS (i) { if a.cells[i] != b.cells[i] { return false; } }
     true
 }
 
@@ -120,7 +120,7 @@ main :: () -> s32 {
     t.expect(c.depth == depth, "cascade: resolve depth matches manual loop");
     same_counts := c.cleared.len == counts.len;
     if same_counts {
-        for 0..counts.len: (i) {
+        for 0..counts.len (i) {
             if c.cleared.items[i] != counts.items[i] { same_counts = false; }
         }
     }